This invention relates to viral proteins and glycoproteins, to compositions containing these proteins, to methods of preparing the proteins, and to their use in detecting viral infection.
Human immunodeficiency virus (HIV) is the etiological agent of acquired immunodeficiency syndrome (AIDS) (Montagnier et al., 1984). To date, two related but distinct viruses HIV-1 and HIV-2, have been identified (Barre-Sinoussi et al., 1983; Brun-Vezinet et al., 1987; Clavel et al., 1986a, 1986b; Guyader et al., 1987; Popovic et al., 1984; Ratner et al., 1985; Wain-Hobson et al., 1985). HIV-2 is closely related to simian immunodeficiency virus (SIV-mac), which causes an AIDS-like disease in macaques (Daniel et al., 1985; Fultz et al., 1986; Chakrabarti et al., 1987). Alignments of the nucleotide sequences of HIV-1, HIV-2, and SIV reveal a considerable homology between HIV-2 and SIV-mac. These two viruses share about 75% overall nucleotide sequence homology, but both of them are only distantly related to HIV-1 with about 40% overall homology (Guyader et al., 1987; Chakrabarti et al., 1977).
In addition to the genes that encode structural proteins (the virion capsid and envelope glycoproteins) and the enzymes required for proviral synthesis and integration common to all retroviruses, HIV-1, HIV-2, and SIV encode genes that regulate virus replication as well as genes that encode proteins of yet unknown function. The only notable difference in the genetic organizations of HIV-1, HIV-2, and SIV resides in the open reading frame referred to as vpx, which is absent in HIV-1 and vpu in HIV-1 but not in HIV-2 and SIV (Cohen et al., 1988; Guyader et al., 1987). These viruses are both tropic and cytopathic for CD4 positive T lymphocytes (Klatzmann et al., 1984; Clavel et al., 1985a; Dalgleish et al., 1984; Daniel et al., 1985). A great number of studies have indicated that CD4 functions as the cellular receptor of HIV (Weiss, 1988).
The HIV-1 env gene encodes a 160-kilodalton (kDa) glycoprotein that is proteolytically cleaved to yield the extracellular and transmembrane proteins, gp120 and gp41, respectively (Montagnier et al., 1985). Similarly, HIV-2 env gene encodes a precursor glycoprotein which is then processed to the mature extracellular and transmembrane glycoproteins (Rey et al., 1989). However, unlike HIV-1, the processing of HIV-2 envelope precursor gp140 seems to require the formation of a homolgous dimer (gp300) during its processing. Interestingly, dimerization of the envelope precursor is also observed in SIV infected cells (Rey et al. 1989). Accordingly, dimer formation seems to be a specific property of HIV-2 and SIV envelope gene expression.
There exists a need in the art for additional information on the structure and in vivo processing of HIV-2 proteins, and especially HIV-2 envelope proteins and glycoproteins. Such information would aid in identifying HIV-2 infection in individuals. In addition, such findings could aid in elucidating the mechanism by which HIV-2 infection and virus proliferation occur and thereby make it possible to devise modes of intervening in viral processes.
This invention aids in fulfilling these needs in the art by providing HIV-2 envelope proteins and glycoproteins in purified form. More particularly, this invention relates to the processing of HIV-2 envelope glycoproteins and the characterization of the transmembrane glycoprotein. Previously, the detection of the transmembrane glycoprotein had been handicapped by the lack of specific antibodies. For this reason, polyclonal antibodies were prepared against the purified HIV-2 envelope precursor. Furthermore, monoclonal antibodies were prepared against a synthetic polypeptide deduced from the sequence of the transmembrane glycoprotein of HIV-2. With the help of these antibodies the membrane glycoproteins of HIV-2 and SIV were identified.
It was discovered that the transmembrane proteins exist as a homodimer in the infected cells as well as in the virions. Dimeric forms of the transmembrane glycoproteins of HIV-2 and SIV can be dissociated in an ionic detergent to 36 kDa and 32 kDa proteins, respectively. Conformational modifications brought about by the formation of envelope precursor might be necessary for transport of the glycoprotein precursor to the Golgi apparatus and its processing into the mature glycoprotein products, the extracellular and transmembrane envelope proteins. Futhermore, the transmembrane dimer might be essential for optimal structure of the virion and thus its infectivity.
This invention thus provides gp80 structural glycoprotein of HIV-2 dimeric form of the transmembrane glycoprotein and human retroviral variants of HIV-2 containing the structural glycoprotein in purified form.
A similar high molecular weight glycoprotein of Simian Immunodeficiency Virus (SIV) or of a Simian retroviral variant of SIV has also been discovered. This glycoprotein is the dimeric form of transmembrane glycoprotein of SIV and has an apparent molecular weight of about 65 kDa (gp65SIV). This glycoprotein is also provided in a purified form.
This invention also provides labeled gp80 of HIV-2 and gp65 of SIV. Preferably, the labeled glycoproteins are in purified form. It is also preferred that the labeled glycoprotein is capable of being immunologically recognized by human body fluid containing antibodies to HIV-2 or SIV. The glycoproteins can be labeled, for example, with an immunoassay label selected from the group consisting of radioactive, enzymatic, fluorescent, chemiluminescent labels, and chromophores.
Immunological complexes between the proteins and glycoproteins of the invention and antibodies recognizing the proteins and glycoproteins are also provided. The immunological complexes can be labeled with an immunoassay label selected from the group consisting of radioactive, enzymatic, fluorescent, chemiluminescent labels, and chromophores.
Furthermore, this invention provides a method for detecting infection of cells by human immunodeficiency virus type-2 (HIV-2). The method comprises providing a composition comprising cells suspected of being infected with HIV-2, disrupting cells in the composition to expose intracellular proteins, and assaying the exposed intracellular proteins for the presence of gp80 glycoprotein of HIV-2. The exposed intracellular proteins are typically assayed by electrophoresis or by immunoassay with antibodies that are immunologically reactive with gp80 glycoprotein of HIV-2.
This invention provides still another method of detecting antigens of HIV-2, which comprises providing a composition suspected of containing antigens of HIV-2, and assaying the composition for the presence of gp80 glycoprotein of HIV-2. The composition is typically free of cellular debris. The molecular weight of the gp80 is estimated more or less 10%. The same for the other molecular weight mentioned in the present invention.
A method of distinguishing HIV-2 infection from HIV-1 infection in cells suspected of being infected therewith has also been discovered. The method comprises providing an extract containing intracellular proteins of the cells, and assaying the extract for the presence of gp80 glycoprotein. The gp80 is characteristic of HIV-2, but the glycoprotein has not been found in extracts of HIV-1 cell cultures.
In addition, this invention provides a method of making gp80 glycoprotein of HIV-2, which comprises providing a composition containing cells in which HIV-2 is capable of replicating, infecting the cells with HIV-2, and culturing the cells under conditions to cause HIV-2 to proliferate. The cells are then disrupted to expose intracellular proteins. The gp80 glycoprotein is recovered from the resulting exposed intracellular proteins. It could be also recovered by detergent solubilization of HIV-2 virions.
This invention also provides an in vitro diagnostic method for the detection of the presence or absence of antibodies which bind to an antigen comprising the proteins or glycoproteins of the invention or mixtures of the proteins and glycoproteins. The method comprises contacting the antigen with a biological fluid for a time and under conditions sufficent for the antigen and antibodies in the biological fluid to form an antigen-antibody complex, and then detecting the formation of the complex. The detecting step can further comprise measuring the formation of the antigen-antibody complex. The formation of the antigen-antibody complex is preferably measured by immunoassay based on Western Blot technique, ELISA (enzyme linked immunosorbent assay), indirect immunofluorescent assay, or immunoprecipitation assay.
A diagnostic kit for the detection of the presence or absence of antibodies which bind to the proteins or glycoproteins of the invention or mixtures of the proteins and glycoproteins contains antigen comprising the proteins, glycoproteins, or mixtures thereof and means for detecting the formation of immune complex between the antigen and antibodies. The antigens and the means are present in an amount sufficient to perform the detection.
This invention provides a method of preparing envelope transmembrane glycoproteins, which comprises providing an extracellular composition containing gp80 glycoprotein of HIV-2 or gp65 of SIV and then dissociating the glycoprotein of HIV-2 or the glycoprotein of SIV. A non-glycosylated dimeric form of the transmembrane envelope protein of HIV-2 (and SIV) can be obtained from the glycosylated form of gp80 (or gp65) by using specific enzymes (i.e. endo F), which cleave mature oligosaccharide chains. Another procedure for the production of unglycosylated forms of such dimeric protein could be genetic engineering methods (see Reference 16).
This invention also provides an immunogenic composition comprising a protein or glycoprotein of the invention in an amount sufficient to induce an immunogenic or protective response in vivo, in association with a pharmaceutically acceptable carrier therefor. A vaccine composition of the invention comprises a neutralizing amount of the dimeric transmembrane envelope glycoprotein or unglycosylated form thereof and a pharmaceutically acceptable carrier therefor.
The dimeric form of the transmembrane glycoprotein is highly recognized by all sera positive for HIV-2 antigens. Therefore, the detection of gp80 could be used as a marker for characterization of HIV-2 positive sera and for differentiation from HIV-1 positive sera.
The proteins and glycoprotein of this invention are thus useful as a portion of a diagnostic composition for detecting the presence of antibodies to antigenic proteins associated with HIV-2 and SIV. In addition, the proteins and glycoproteins can be used to raise antibodies for detecting the presence of antigenic proteins associated with HIV-2 and SIV. The proteins and glycoproteins of the invention can be also employed to raise neutralizing antibodies that either inactivate the virus, reduce the viability of the virus in vivo, or inhibit or prevent viral replication. The ability to elicit virus-neutralizing antibodies is especially important when the proteins and glycoproteins of the invention are used in vaccinating compositions.